This application is related to application Ser. No. 107,309 filed Aug. 17, 1993 that is owned by the assignee of this application.
The present invention relates to packaging for semiconductor devices, and more particularly to packages and methods of packaging high power semiconductor devices in which the size and weight of the package are reduced, heat transfer from the semiconductor device is increased, and hermetic seals may be more easily made.
High power semiconductor devices such as thyristors, diodes, and the like that may conduct thousands of amperes of current and may operate at thousands of volts are finding increased application in commercial power transmission. Typically, such devices are used as fast acting switches that prevent a drop in power when there is an interruption in the line, although the uses are myriad and the present invention is non so limited.
The semiconductor devices are usually packaged to protect them from the environment in which they operate, although the packages desirably also afford reasonable access to the devices inside so that electrical connections can be made, are compact in size and lightweight, and do not hinder heat conduction away from the devices. Of these, heat conduction presents the more vexing problem as high power semiconductor devices conducting a thousand amperes or more may generate more than a kilowatt of heat in their silicon substrates, while the operating temperature is to be kept at less than 150.degree. C. The packages are also desirably sealed to prevent exposing the devices to humidity, oxygen, dust, etc., such seals being referred to herein as hermetic. As is apparent, such seals may exacerbate the heat conduction problem.
While these desirable packaging characteristics may be relatively easy to design for some low power devices that do not generate much heat and that operate in benign environments, high power semiconductor devices that may be exposed to the elements in remote locations present a considerable packaging challenge. Prior art packages for high power semiconductor devices may adequately address one of these characteristics, but none reasonably address them all. For example, the package disclosed in U.S. Pat. No. 3,723,836 issued Mar. 27, 1973 to Shekerjian, et al. does not afford easy access to the semiconductor devices inside and does not provide sufficient thermal conductivity. The device in U.S. Pat. No. 5,248,901 issued Sep. 28, 1993 to V. A. K. Temple, one of the inventors hereof, uses a flange that adds a manufacturing step.
Accordingly, it is an object of the present invention to provide a novel package and method of packaging a semiconductor device that obviate the problems of the prior art.
It is another object of the present invention to provide a novel hermetic package and method of hermetically packaging a semiconductor device in which the package is compact and lightweight, and easy to manufacture.
It is yet another object of the present invention to provide a novel package for a semiconductor device that allows heat to be dissipated from two sides of the device while affording access for electrical connections to those two sides.
It is a further object of the present invention to provide a novel compact package for a semiconductor device that provides access to electrical contacts for the device through openings in a ceramic base and through a metal lid that is bonded to the base.
It is still a further object of the present invention to provide a novel packaged semiconductor device in which the device is protected by a metal lid and a similarly sized ceramic base that are bonded together an their edges to form a hermetic seal and in which heat from the device is conducted through both the lid and the base.